Which chemical process affects the cortex of the hair?

The coloring process is the correct choice because it involves the application of chemical agents that penetrate the cortex of the hair. The cortex is the middle layer of the hair strand, containing melanin (the natural pigment) and keratin. Different coloring products, such as permanent and semi-permanent dyes, utilize various chemicals to lift the cuticle (the outer layer) and allow the coloring agents to enter and alter the pigment in the cortex, leading to changes in color.

In contrast, other processes like the hygroscopic process refer to the absorption of moisture and do not involve a chemical change in the hair structure. The shampooing process primarily aims to cleanse the hair and scalp, affecting mostly the surface and not the inner cortex. The cutting process modifies the length of the hair but does not influence the structure or pigmentation of the hair at a chemical level. Therefore, the coloring process is uniquely positioned as the method that chemically alters the cortex of the hair.